Apparatus for stripping coaxial cable

ABSTRACT

An apparatus and method for removing a measured portion of insulation from the end of a miniature solid-jacketed, coaxial cable, the apparatus including a spray chamber having an orifice containing a hermetic seal assembly for the insertion and support of the end of the cable, a precisely adjustable stop member for determining the length of cable to be inserted into the chamber, a spray assembly for applying etchant to the inserted portion, a switch in the face of the stop member for automatically actuating the spray assembly upon insertion of the proper length of the cable into the chamber and an adjustable timing mechanism for controlling the amount of etchant applied to remove the metal sheath. The exposed dielectric insulation is thermally removed, and the conductor cleaned and trimmed to the desired length.

United States Patent Paulin [451 Aug. 20, 1974 APPARATUS FOR STRIPPING COAXIAL CABLE Inventor: Howard Douglas Paulin, Broomall,

Assignee: Burroughs Corporation, Detroit,

Mich.

Filed: Sept. 20, 1972 Appl. No.: 290,774

US. Cl 156/345, 156/3, 156/16 Int. Cl. C231 1/02 Field of Search 156/3, 7, 16, 345;

References Cited UNITED STATES PATENTS 9/1956 Edds 156/7 9/1966 Schroeder 156/16 X Primary Examiner-William A. Powell Attorney, Agent, or Firm-Alan Petlin Klein; Edmund M. Chung; Charles S. Hall ABSTRACT An apparatus and method for removing a measured portion of insulation from the end of a miniature solidjacketed, coaxial cable, the apparatus including a spray chamber having an orifice containing a hermetic seal assembly for the insertion and support of the end of the cable, a precisely adjustable stop member for determining the length of cable to be inserted into the chamber, a spray assembly for applying etchant to the 9 Claims, 8 Drawing Figures 00 IIIIIII\XIII lIIIIIIIII/IIIIIIVIIIII'IYIIII PUMP HlSS

TIMER /6I PAIENIEBmzomu SIEHINZ iFI' Pmmm wczmsu am am 2 NOCONTACT RESET CONTACT START AC. POWER SUPPLY APPARATUS FOR STRIPPING COAXIAL CABLE BACKGROUND OF THE INVENTION The invention relates generally to an improved apparatus and method for preparing cables for connection to associated electronic apparatus, and more particularly to a process for removing concentric insulation and of severing, without deformation, a concentric conductor around a central conductor, such conductors being in the field of solid-jacketed coaxial cables.

With the advent of micro-miniaturization and high speed pulse networks, such as those found in present day computers, the trend towards lighter and more compact electronic assemblies has led to a demand for thinner electrical conductors. Miniature solid-jacket coaxial cables have met this demand. However, regardless of the diameter of the type of conductor the difficulties encountered in preparing insulated conductors for connection to associated apparatus are still ever present.

As a standard practice in the manufacture of complex electronic systems, considerable care and energy is expended in stripping the insulation from the ends of an electrical conductor in a manner whereby there is no degradation of the electrical characteristics of the conductor. This aspect is especially important when working with solid-jacket coaxial cables, and becomes more acute as the diameter of this type of cable becomes smaller.

Solid-jacketed coaxial cables presently used in the electrical and electronic industry generally consist of a single center conductor, such as a copper wire, surrounded by a dielectric plastic material such as neoprene, nylon, tetrafluoroethylene (Teflon Trademark of the DuPont Company), etc. The plastic material is enclosed in a very close and accurate relationship with a solid metal jacket or sheath, which, in most instances, is essentially an outer conductor of copper tubing. The insulating material serves not only as insulation, but also to accurately maintain a given distance of the center conductor from the outer jacket conductor. This spatial relationship between the center conductor and the outer jacket conductor is extremely important in those situations where two conductors are required to transmit a high frequency signal accurately. It is because of this spatial relationship that the cable possesses a uniform electrical impedance, which is a prerequisite in high speed pulse networks. Any physical degradation of the cable would destroy this uniformity of impedance, and, thus, its applicability in a given circurt.

In making connections to solid-jacketed coaxial cables, a length of the center conductor must be completely exposed from its insulation and the surrounding metal jacket or sheath. Presently, the most prevalent method of stripping smaller diameter solid-jacket coaxial cables is by simply cutting the outer metal jacket or sheath with a sharp blade or like apparatus, and then by brute force pull the outer sheath or jacket from the insulation. The uncovered insulation is then removed to expose the center conductor. With larger diameter cables, it is the practice in the art to utilize cutting pliers, cable cutters, pocket knives and similar apparatus for cutting and stripping both the outer jacket and the insulation from the cable. Also, mechanical strippers,

which automatically perform themanual function of cutting and stripping are popular 'with cables of sufficient diameter.

However, irrespective of the diameter of the cable, in order to maintain the proper electrical characteristics of the cable, it is essential that the remaining outer metal jacket or sheath not be damaged as, for example, by being deformed or having its edges flared as will result from a tubing cutter, or having any other distortion which affects the uniform distribution of the outer metal jacket about the center conductor. Moreover, it is desired that the center conductor be undamaged, as the slightest nick or scratch caused by penetrating too deeply with the cutting apparatus drastically increases the susceptibility of the conductor to breakage.

Furthermore, considering present day'requirements, it is readily apparent that as the diameter of the cable decreases, the slightest damage to the cable has a greatly amplified effect on the cable. The probability of such damage occurring is likely when the method and apparatus presently found in the art are utilized. Thus, the present invention is primarily directed towards a method and apparatus which efficiently and economically prepares small diameter or miniature solid-jacket cables for connection without any degradation to the cable.

Accordingly, it is a primary object of this invention to reduce the possibility of physical distortion to solidjacketed coaxial cables during stripping.

Another object of this invention is, the simple, efficient and reliable removal of the outer sheath or jacket from solid-jacketed cable with particular reference to miniature coaxial cables.

Another object of this invention is to insure unifor- I mity of stripping of terminal portions of coaxial cables.

A further object of this invention is to provide a work-actuated apparatus for removing the sheath or jacket from solid-jacketed cable.

A still further object of this invention resides in the provision of a spray apparatus for exposing a predetermined portion of a solid-jacketed cable to a chemical etchant.

Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specifications and appended claims.

SUMMARY OF THE INVENTION The apparatus of the invention removes the outer metal jacket or sheath of the cable with the aid of chemical action. The end of the cable is inserted into an orifice of a seal assembly, mounted in a side wall of a spray chamber, until the end cross sectional surface of the inserted cable abuts a stop, which has been prepositioned to the length of the outer jacket desired to be removed. Physical contact of the cable with the stop actuates a pump for urging a spray of chemical etchant against the outer metal jacket of the cable. Simultaneously, a pre-set timing mechanism is actuated which controls the duration of the pumping cycle. The seal assembly provides not only support for the inserted cable but also screens a portion of the outer jacket which is not to be removed.

In accordance with the method of the invention, the outer metal jacket and inner plastic insulation are removed from the solid-jacketed coaxial cable with a BRIEF DESCRIPTION OF THE DRAWINGS A.clear conception of the features constituting the present improvement and of the construction and operation of the apparatus embodying the invention may be gained by referring to the drawings accompanying the specification, wherein like reference characters designate the same or similar parts in the various views.

FIG. 1 is a perspective view of the end of a solid- I jacketed coaxial cable;

FIG. 2 is a perspective view of the end of the solidjacketed cable of FIG. 1 after having the outer metal jacket removed by the apparatus of this invention;

FIG. 3 is a perspective view of the end of a solidjacketed coaxial cable of FIG. 1 prepared through the method of this invention;

FIG. 4 is a side-sectional view of the apparatus of the invention;

FIG. 5 is an end-sectional view of the apparatus of the invention;

FIG. 6 is an enlarged sectional view of the seal assembly of FIG. 4;

FIG. 7 is a sectional view of an insert for the seal assembly of FIG. 6;

FIG. 8 is a schematic diagram of the electrical circuitry for the apparatus of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT bore 23 are annular recesses 25 in which are seated 0- rings 33. With the insertion of the cable 10, the O-rings 33 are forced into the recesses 25 to form an air-tight seal around the outer jacket 13 of the cable 10. Seal assembly 29 serves not only to position and align the selected end portion 14 of the cable 10, but also supports the cable 10 while inserted in the apparatus.

While the diameter of the axial bore 23 of the seal assembly 29 is the limiting factor as to the size of cable that can be inserted'into the apparatus, a plurality of seal assemblies 29 having axial bores of various diameters may be selectively utilized. For very small diameter cables a flexible insert 50 shown in FIG. 7, having a stem portion 52, a shank portion 54, and an axial bore 51 can be inserted into the seal assembly 29. The stem portion 52, which is larger than the shank portion 54, is provided for easy insertion and-removal of the flexible insert 50. The O-rings 33 of the seal assembly 29 form an air-tight seal around the shank'portion 54 of the insert 50. Insert 50 is specifically designed so that the end cross'sectional surface 53 of shank portion 54 Moreover, the etching apparatus is designed so that the pressure inside the etching chamber 31 is at approximately the atmospheric pressure, to reduce the danger of etchants being forced around the cable 10 into the axial bore 51 of the insert 50.

The travel of cable 10 into the etching chamber 31 is regulated by a movable stop 34 secured to one end A solid-jacketed coaxial cable 10 (FIGS. l-3) is norv mally comprised of a copper center conductor 11 surrounded by a plastic insulation 12 and a copperjacketed sheath l3 enclosing the plastic insulation material l2 and concentric to the center conductor 11. In preparing the cable 10 for connection to the associated circuitry or apparatus, an area 14 of the outer sheath l3 and a portion of the plastic insulation material 12 must be removed to expose the center conductor 11.

An apparatus for etching a selected portion of the outer jacket 13 of the cable 10 is shown in FIGS. 4 and 5. The apparatus includes a suitable housing 30 for a cylindrical etching chamber 31, having circular end panels 39 and 40. The end panels 39, 40 have raised internal circular portions 41 which are designed to form a hermetic seal with the cylindrical portion of the etching chamber 31. The etching chamber 31, as well as other parts of the apparatus to be described, which are exposed to a chemical etchant, are fabricated from a material, preferably Teflon or characteristically similar material, which is inert to the etchant.

The solid-jacketed cable 10 which is to have a selected end portion 14 of the outer metal jacket 13 removed, is axially inserted into the etching apparatus through an orifice 32 of a seal assembly 29 which is mounted in the front panel 39 by cap screws 28 or other suitable means. Orifice 32, FIG. 6, has a tapered mouth portion 24 leading into an axial bore 23, which serves to guide the cable 10 into the chamber 31. Located near the mouth 24 and an exit 27 of the axial ofa rod 45. Rod 45, having calibrations 46 thereon, passes through the rear panel 40 of the etching chamber 31, and is threaded through a casing and a sea] assembly 56. A hand knob 35, external to the etching chamber 31 is secured to the outer end of the rod 45 to provide precise manual control for the positioning of the movable stop 34. The calibrations 46 on the rod 45 coincide with the selected length of the outer jacket 13 to be removed. In addition, the longitudinal axis of the rod 45 coincides with the longitudinal axis of the axial bore 23 of the seal assembly 29.

The movable stop 34 houses a microswitch which is electrically connected in series-with a timing mechanism 61 (FIG. 5). The timing mechanism 61 is set according to the thickness of the selected portion of the copper-jacket to be removed, which in turn is ordinarily dependent upon the cable size. Upon contact of the end portion 14 of the cable 10 with the movable stop 34, microswitch 60 completes an electrical circuit 58 (FIG. 8) which activates a cycle of the timing mechanism 61. Similarly, activation of the timing mechanism 61 completes an electrical circuit 59, which supplies electric current to a pump 62 which urges a flow of chemical etchant to a circular spray manifold 37. An indicator lamp 49 may be lighted for the duration of the timing cycle. Upon completion of the timing cycle, the supply of electrical current is discontinued to pump 62 and the flow of etchant to manifold 37 is stopped. However, timing mechanism 61 is not reset until the cable 10 is removed from contact with the movable stop 34.

The circular spray manifold 37 is mounted on the cylindrical portion of the etching chamber 31 as by brackets 38. The manifold 37 feeds a plurality of spray nozzles 36 oriented in quadrants to provide complete coverage of the end portion 14 of cable inserted in the apparatus. The nozzles 36 are positioned so as to direct a spray of chemical etchant inwardly toward the center of the etching chamber 31 and the selected portion of the outer jacket 13 of the cable 10. The center of the circular manifold 37 coincides with the longitudinal axis of the seal assembly 29.

A flow of chemical etchant is supplied to the manifold 37 through a hose 47 which is connected at one end to the manifold 37 via an inlet port 48 to the etching chamber 31, and at the other end to pump 62. The chemical etchant emanates from the pump 62 and is returned to pump 62 through a return hose 43 via outlet port 44 located near the bottom of the housing 30. The chemical etchant, after being discharged from the spray nozzles 36 and directed towards the selected end portion 14 of the cable 10, collects at the bottom of the etching chamber 31. A drain 42, located at the bottom of the etching chamber 31, feeds the outlet portion 44.

The chemical etchant may be recycled many times before the quantity of dissolved copper adversely affects the etching properties of the etchant. In such a situation, fresh chemical etchant is admitted into the system via a control valve 57 connected in hose 47, while spent chemical etchant is discharged through a control valve 53 connected in the return hose 43.

To insure the complete removal of all etchant from the cable 10 before extracting the cable 10 from the apparatus, a stream of air may be directed toward the end portion 14 of cable 10 after the etching cycle. Air may be supplied directly to the spray manifold 37 through an appropriate control valve 63 located near the inlet port 48, and escape from the etching chamber through air vents of known design.

A neutral liquid may also be used to remove all remaining traces of the chemical etchant. However, if it is desired that the etchant be recycled for use again, a control valve (not shown) must be provided in return hose 43 to divert the neutral liquid. lf ordinary tap water is used, it would be quite easy to utilize control valve 63 so that water directly from the tap may be fed to the spray manifold after the flow of etchant without an additional pump.

In operation, the apparatus disclosed could easily be bench mounted or portable. Flexible housing can be provided for facilitating ease in movement for the apparatus.

It will be noted that although this apparatus is primarily designed to accommodate small diameters and miniature size solid-jacketed cables, it will be apparent to those familar with the art that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof.

In carrying out the method of the invention the portion of the outer jacket 13 of the cable 10 which is not to be removed is screened to prevent exposure to an etchant spray. A precisely measured unscreened portion 14 of the outer jacket 13 of the cable 10 is then exposed to a spray of chemical etchant, such as chromic sulphuric acid or any other suitable commercial chemical stripper for copper, to uncover a section 15 of the plastic insulation material 12. Following the removal of the measured portion of the outer jacket 13, a portion 16 of the uncovered plastic insulation material 12 is removed by a suitable commercial thermal-stripper or in the alternative, high frequency heating (e.g., infrared radiation) can be utilized. After removal of a portion of the insulation material 12, the exposed center conductor is cleaned, rinsed and trimmed to the desired length.

The process of this invention virtually eliminates any possibility of physical damage to the solid-jacketed coaxial cable 10 during the preparation of the cable for connection. The removal of the outer metal jacket 13 is achieved without the aid of any sharp instruments or apparatus which can smash or deform the concentric distribution of the outer jacket 13 around the center conductor 1 1, or which can damage the center conductor 13 itself.

This method is particularly useful with small diameter or miniature solid-jacketed coaxial cables, where ease in handling becomes an important consideration.

As the diameter of cable 10 decreases the use of metive, the scope of the invention being indicated by the appended claims.

What is claimed is:

1. An apparatus for removing a selected length of the outer metal jacket of solid-jacketed type cable comprising:

a chemical etchant spray chamber;

orifice means for sealably inserting an end of said cable into said spray chamber; and

adjustable means mounted in a wall of said spray chamber for predetermining the length of said cable to be inserted into said chamber.

2. The apparatus of claim 1 wherein said adjustable means is mounted in a wall of said spray chamber opposite said orifice means and wherein said adjustable means includes a rod extending outside said chamber and threadably engaged therewith.

3. The apparatus of claim 2 including calibration on the portion of said rod extending outside said chamber for measuring the predetermined length of the jacket to be removed.

4. The apparatus of claim 2 wherein said orifice means has a longitudinal axis for positioning and supporting said cable and wherein said longitudinal axis is aligned with the longitudinal axis of said rod.

5. The apparatus of claim 1 wherein said orifice means include means for accommodating cables of different diameters.

6. The apparatus of claim 5 wherein said means for accommodating cables of different diameters includes selectable inserts having cylindrical apertures of circular cross section, and including O-rings emplaced in said cylindrical apertures.

7. The apparatus of claim 6 wherein said means for accommodating cables of different diameters also includes one plug having a bore of circular cross section therethrough for insertion into the cylindrical aperture of a selected one of said inserts.

8 9. The apparatus of claim 3 wherein said adjustable means include:

means responsive to the insertion of said selected length of said cable for actuating said urging means 

1. An apparatus for removing a selected length of the outer metal jacket of solid-jacketed type cable comprising: a chemical etchant spray chamber; orifice means for sealably inserting an end of said cable into said spray chamber; and adjustable means mounted in a wall of said spray chamber for predetermining the length of said cable to be inserted into said chamber.
 2. The apparatus of claim 1 whErein said adjustable means is mounted in a wall of said spray chamber opposite said orifice means and wherein said adjustable means includes a rod extending outside said chamber and threadably engaged therewith.
 3. The apparatus of claim 2 including calibration on the portion of said rod extending outside said chamber for measuring the predetermined length of the jacket to be removed.
 4. The apparatus of claim 2 wherein said orifice means has a longitudinal axis for positioning and supporting said cable and wherein said longitudinal axis is aligned with the longitudinal axis of said rod.
 5. The apparatus of claim 1 wherein said orifice means include means for accommodating cables of different diameters.
 6. The apparatus of claim 5 wherein said means for accommodating cables of different diameters includes selectable inserts having cylindrical apertures of circular cross section, and including O-rings emplaced in said cylindrical apertures.
 7. The apparatus of claim 6 wherein said means for accommodating cables of different diameters also includes one plug having a bore of circular cross section therethrough for insertion into the cylindrical aperture of a selected one of said inserts.
 8. The apparatus of claim 1 wherein said spray chamber includes: means for urging a flow of said etchant spray against said inserted predetermined length of said cable; and means for regulating the duration of said urging means.
 9. The apparatus of claim 3 wherein said adjustable means include: means responsive to the insertion of said selected length of said cable for actuating said urging means. 